Conventionally, microcapsule formulations are known as sustained-release formulations of pesticidal compounds. Several methods are known as techniques of microencapsulating pesticidal compounds. An interfacial polymerization method is used favorably because it is easy to control the coating film thickness of microcapsules and therefore it is easy to adjust the sustained-release performance of pesticidal compounds appropriately. Microencapsulation by the interfacial polymerization method is disclosed, for example, in Japanese Patent Laid-Open Nos. 5-201814 and 8-99805.
Usually, in the event that a water-insoluble pesticidal compound can be dissolved in a water-insoluble organic solvent, it is possible to obtain microcapsules by dispersing a solution of the pesticidal compound in the organic solvent to form liquid droplets in water and forming a coating film of a resin by polymerization at the interfaces between the liquid droplets and water. In the case of a highly water-soluble pesticidal compound, however, it is difficult to make the pesticidal compound be enclosed sufficiently in microcapsules by such interfacial polymerization or in-situ polymerization because the pesticidal compound adversely dissolves in water.